In a wireless network, e.g., an ad hoc network, in which a network infrastructure does not exist, a terminal has to combat certain challenges in order to set up a communication link with another peer terminal. One challenge is that when a terminal just powers up or moves into a new area, the terminal may have to first find out whether another terminal is present in the vicinity before any communication between the two terminals can start.
The general solution to the above problem of identification and acquisition is to let the terminal transmit and/or receive signals according to certain protocol. Note that the protocol and the signal have to be designed carefully so that the solution is robust and power efficient. Robustness is essential. For example, the terminals often may not have a common timing reference, e.g., because of the lack of the network infrastructure. So it is possible that when a first terminal is transmitting a signal and a second terminal is not in the receiving mode, the transmitted signal does not help the second terminal to detect the presence of the first terminal. Power efficiency has great impact on the battery life of the terminals and is thus another important issue in the wireless system.
In addition to solving the above problem of identification and acquisition, the terminals need to be synchronized with each other to enable proper peer-to-peer communication.
In view of the above discussion, it should be appreciated that there is a need for new and improved ways for identification, acquisition or synchronization, especially in a wireless system in which the network infrastructure is not available.